feat(grok): improve free quota probing and usage

frontend/src/i18n/locales/en/admin/accounts.ts

@@ -1202,6 +1202,7 @@ export default {
         claude: 'Claude',
         grokRequests: 'Req',
         grokTokens: 'Tok',
+        grokWeeklyUsage: 'Weekly {percent}%',
         grokUnknown: 'Grok quota is unknown until the first upstream response includes xAI rate-limit headers.',
         grokRetryAfter: 'Retry after {time}',
         grokProbe: 'Probe',

frontend/src/i18n/locales/zh/admin/accounts.ts

@@ -317,6 +317,7 @@ export default {
         claude: 'Claude',
         grokRequests: '请求',
         grokTokens: 'Token',
+        grokWeeklyUsage: '周额度已用 {percent}%',
         grokUnknown: 'Grok 配额需等待首次上游响应返回 xAI rate-limit 头后显示。',
         grokRetryAfter: '{time} 后重试',
         grokProbe: '探测',